e-MERLIN's deep radio survey of the Hubble Deep Field: first results

27 March 2012

Caption: Image composed from e-MERLIN and EVLA observations in C-band. The width
of the whole field is approximately 1/4 of a degree (the same diameter as half a
full moon). The inset images illustrate the effectiveness of e-MERLIN's
capabilities in revealing the structure of galaxies even at distances of
billions of the light years. Bottom left: An interesting example of an AGN
galaxy with large lobes thought to be caused by jets, emanating from a central
black hole, interacting with interstellar material. Bottom right: An FR1 type
AGN galaxy. Top left: A more typical AGN type galaxy. Top right: An AGN with
star formation characteristic emission detected at an estimated distance of 7.5
billion light-years. Credit: N. Wrigley / Jodrell Bank Centre for Astrophysics

A team of astronomers at Jodrell Bank Observatory have begun the deepest ever
high-resolution radio imaging of the region around the Hubble Deep Field (HDF),
the images originally captured by the Hubble Space Telescope (HST) in the mid
1990s. The HDF led to the discovery of numerous galaxies billions of light years
distant and provided direct visual evidence of the evolution of the Universe.
First results from the new imaging, which uses observations from the UK's newly
upgraded e-MERLIN radio telescope array together with the EVLA radio array based
in New Mexico, show galaxies some 7 billion light years away in unprecedented
detail. Graduate student Nick Wrigley will present the new results at the
National Astronomy Meeting in Manchester on 27 March 2012.

e-MERLIN is an array of radio telescopes distributed across the United Kingdom
connected together by optical fibres. Data from each telescope is sent across
this network to Jodrell Bank where a device known as a 'correlator' processes
them into a single image. This technique, known as interferometry, simulates a
single radio telescope hundreds of kilometres across and produces exceptionally
sharp images of astronomical objects.

EVLA is a similar more compact array in New Mexico in the United States that
shows the coarser structure of objects and complements the e-MERLIN
observations. The two arrays started to survey the HDF region in 2011 and the
team expect the project to be completed in the next few years.

The first wide-band images of the whole HDF region capture the brightest objects
in the field at sub-arcsecond resolution, equivalent to being able to
distinguish a ten pence piece at a distance of over 5 kilometres. The pictures
were assembled by Mr Wrigley under the supervision of Dr Rob Beswick and Dr Tom
Muxlow at the Jodrell bank Centre for Astrophysics in Manchester. The image in
the background, observed using the EVLA, shows the unresolved emission from
whole galaxies, whereas the inset images produced using mapping in combination
with e-MERLIN show the fine detail.

The high resolution provided by e-MERLIN allows astronomers to distinguish
between the different types of galaxies, identifying those that have emission
from material being dragged into supermassive black holes (so called Active
Galactic Nuclei or AGNs) and those where the emission originates from rapid star
formation or starbursts. The HDF galaxies are so far away that the light we see
from them left as long ago as 12 billion years ago, so the new radio
observations are giving us an insight into the formation of stars when the
universe was less than 10% of its present age.

This new work is just the start of a multi-year survey of the HDF and provides a
glimpse of the capabilities of wide-band (broadband data transmission) synthesis
imaging now possible with simultaneous use of the e-MERLIN and EVLA arrays.
Crucially, the e-MERLIN and EVLA correlators now generate compatible data
allowing future observations to be combined like never before.

The first images were made with relatively short exposure times, but the whole
project, named e-MERGE (led by Dr. Tom Muxlow (Manchester), Prof. Ian Smail
(Durham) and Prof. Ian McHardy (Southampton)) will include long observations
gathered at various wide-bands within the radio spectrum generating an
unsurpassed combination of sensitivity and detail. The survey will ultimately
measure massive star formation and AGN activity in very distant galaxies,
tracing the development of the stellar populations and black hole growth in the
very first large galaxies. Using the more accurate observations from e-MERLIN,
it will be possible to produce more precise models of the physical process of
star formation within star clusters in such galaxies and help to answer some of
the many questions faced by cosmologists today.

NAM 2012

Bringing together more than 900 astronomers and space scientists, the
National Astronomy Meeting (NAM 2012) will take place from 27-30 March
2012 in the University Place conference centre at the University of
Manchester in the UK. The conference is a joint meeting of the Royal
Astronomical Society (RAS) and the German Astronomische Gesellschaft
(AG) and is held in conjunction with the UK Solar Physics (UKSP: www.uksolphys.org) and
Magnetosphere Ionosphere Solar Terrestrial (MIST: www.mist.ac.uk) meetings. NAM 2012 is
principally sponsored by the RAS, AG, STFC and the University of
Manchester.

The Royal Astronomical Society

The Royal Astronomical Society (RAS: www.ras.org.uk), founded in 1820,
encourages and promotes the study of astronomy, solar-system science,
geophysics and closely related branches of science. The RAS organises
scientific meetings, publishes international research and review
journals, recognizes outstanding achievements by the award of medals
and prizes, maintains an extensive library, supports education through
grants and outreach activities and represents UK astronomy nationally
and internationally. Its more than 3500 members (Fellows), a third
based overseas, include scientific researchers in universities,
observatories and laboratories as well as historians of astronomy and
others.

The Astronomische Gesellschaft (AG)

The Astronomische Gesellschaft (AG: www.astronomische-gesellschaft.de),
founded in 1863, is a modern astronomical society with more than 800
members dedicated to the advancement of astronomy and astrophysics and
the networking between astronomers. It represents German astronomers,
organises scientific meetings, publishes journals, offers grants,
recognises outstanding work through awards and places a high priority
on the support of talented young scientists, public outreach and
astronomy education in schools.

The Science and Technology Facilities Council

The Science and Technology Facilities Council (STFC: www.stfc.ac.uk) is keeping the UK at
the forefront of international science and tackling some of the most
significant challenges facing society such as meeting our future
energy needs, monitoring and understanding climate change, and global
security. The Council has a broad science portfolio and works with the
academic and industrial communities to share its expertise in
materials science, space and ground-based astronomy technologies,
laser science, microelectronics, wafer scale manufacturing, particle
and nuclear physics, alternative energy production, radio
communications and radar. It enables UK researchers to access leading
international science facilities for example in the area of astronomy,
the European Southern Observatory.

Jodrell Bank Centre for Astrophysics

The Jodrell Bank Centre for Astrophysics (JBCA: www.jb.man.ac.uk/) is part of the
School of Physics & Astronomy at the University of Manchester. JBCA is
split over two main sites: the Alan Turing Building in Manchester and
the Jodrell Bank Observatory in Cheshire. At Jodrell Bank Observatory,
the new Jodrell Bank Discovery Centre is a key focus for our work in
public engagement and education. Jodrell Bank is a world leader in
radio astronomy-related research and technology development with a
research programme extending across much of modern astrophysics. The
group operates the e-MERLIN national radio astronomy facility and the
iconic Lovell Telescope, hosts the UK ALMA Regional Centre Node and is
home to the international office of the SKA Organisation. Funded by
the University, the Science & Technology Facilities Council and the
European Commission, it is one of the UK's largest astrophysics
research groups.